Aqueous solutions of poly(N-isopropyl acrylamide) show a lower critical solution temperature. The thermodynamic properties of the system have been evaluated from the phase diagram and the heat absorbed during phase separation and the phenomenon is ascribed to be primarily due to an entropy effect. From viscosity, sedimentation, and light-scattering studies of solutions close to conditions of phase separation, it appears that aggregation due to formation of nonpolar and intermolecular hydrogen bonds is important. In addition, a weakening of the ordering effect of the water-amide hydrogen bonds as the temperature is raised contributes to the stability of the two-phase system.

Solution Properties of Poly(N-isopropylacrylamide)

Rate coefficients of free-radical polymerization deduced from pulsed laser experiments

Intrinsic viscosities and unperturbed dimensions of long chain molecules

A temperature gradient acts like an external field on colloidal suspensions and drives the solute particles to the cold or to the warm, depending on interfacial and solvent properties. We discuss different transport mechanisms for charged colloids, and how a thermal gradient gives rise to companion fields. Particular emphasis is put on the thermal response of the electrolyte solution: positive and negative ions diffuse along the temperature gradient and thus induce a thermoelectric field which in turn acts on the colloidal charges. Regarding polymers in organic solvents, the physical mechanism changes with decreasing molecular weight: high polymers are described in the framework of macroscopic hydrodynamics; for short chains and molecular mixtures of similar size, the Brownian motion of solute and solvent becomes important.

https://iopscience.iop.org/article/10.1088/0034-4885/73/12/126601/pdf

Thermal non-equilibrium transport in colloids

The intrinsic viscosity of biological macromolecules. Progress in measurement, interpretation and application to structure in dilute solution.

Special purification of the monomer and careful preparation of the reaction setup allowed a thorough study of the spontaneous thermal polymerization of methyl methacrylate over a wide range of temperatures (0–140°C). The rates of polymerization are notably lower than the few data previously reported in literature, and the degrees of polymerization slightly higher. The thermal initiation reaction is superimposed by radical production due to the natural ionising radiation (cosmic radiation etc.). This additional initiation becomes significant at temperatures below 60°C. New and more reliable monomer chain transfer constants are given.

Die thermische Polymerisation von Methylmethacrylat, 1. Polymerisation in Substanz

Primary radical termination in polymerization: Evaluation of the characteristic constant

Es wird uber Sedimentations-, Diffusions- und Viskositatsmessungen an Polydimethylsiloxan berichtet. Als Θ-Losungsmittel diente Bromcyclohexan, das bei 28°C die Beziehung 






liefert, sowie als gutes Losungsmittel Toluol von 25°C mit 






Die Reibungs- und Viskositatswerte erlauben die Berechnung des Tragheitsradius r im Θ-Losungsmittel zu rΘ = 0,27·M1/2. Dieser Radius rΘ ist nur etwa um 40% groser als der Radius rf bei vollig freier Drehbarkeit. Die Polydimethylsiloxankette ist folglich sehr flexibel.



Measurements of sedimentation, diffusion and viscosity were performed on polydimethylsiloxanes in a Θ solvent (bromocyclohexane of 28°C.) and in a good solvent (toluene of 25°C.). The molecular weight viscosity relation was determined as 






in bromocyclohexane and as 






in toluene. Friction and viscosity data allow the calculation of the radius of gyration rΘ giving rΘ = 0.27 M1/2. This radius is only 40% greater than the radius rf of a freely jointed chain, showing that the polydimethylsiloxane chain is very flexible.

Hydrodynamisches verhalten gelöster polydimethylsiloxane

The spontaneous polymerization of methyl methacrylate-IV: Formation of cyclic dimers and linear trimers

Technische Methylcellulose wurde fraktioniert und auf ihr Viskositats-, Sedimentations und Diffusionsverhalten in wasriger Losung untersucht. Die Viskositats-Molekularge-wichts-Beziehung fur Methylcellulosen von etwa 28% Methoxylgehalt ergab sich zu 






Der Exponent 0,63 besagt, das Kette relativ eng geknauelt ist. Ihr Verhalten last sich durch die Theorien der Viskositat gut deuten. So ergibt sich nach DEBYE-BUECHE-PETERLIN fur die Knaueldimension (R = Tragheitsradius in A) 






was eine nur schwache Abweichung vom GAUSSschen Knauel mit M1,00 bedeutet.



Das Verhalten der gelosten Methylcellulose wird zusammen mit Messungen an Athylhydroxyathylcellulosen und Cellulosenitraten betrachtet, bei denen starkere Abweichungen vom idealen GAUSS schen Knauel auftreten. Im Vergleich zu Vinylpolymeren sind die Exponenten der Viskositatsbeziehung durchweg hoher (0,63–1,0 statt 0,5–0,8), die zweiten Virialkoeffizienten A2 des osmotischen Druckes scheinen fast unabhangig vom System Derivat-Losungsmittel zu sein.



Technical methylcellulose was fractionated; intrinsic viscosities, diffusion and sedimentation coefficients in aqueous solution were determined. The viscosity-molecular weight relation for samples of methoxyl content of about 28% resulted as 






The power 0.63 means a relativ compact coil, the dimensions of which can be calculated according to the viscosity theories. Using the theory of DEBYE-BUECHE-PETERLIN we found for the dimension of the coil with R = radius of gyration in [A] 






This means only a slight deviation from the ideal GAUSSian coil with M1,00.



The behaviour of the methylcellulose in solution is discussed together with measurements on ethylhydroxyethylcellulose and eellulosenitrate, which show a more pronounced deviation from the ideal GAUSSian coil. In comparison to vinyl polymers the exponents of the viscosity-relation are higher (0.63—1.0 instead of 0.5—0.8), the second osmotical virial coefficient A2 seems to be independent of the system derivative – solvent.

G. Meyerhoff

Papers

Die thermische Polymerisation von Methylmethacrylat, 1. Polymerisation in Substanz

Primary radical termination in polymerization: Evaluation of the characteristic constant

Hydrodynamisches verhalten gelöster polydimethylsiloxane

The spontaneous polymerization of methyl methacrylate-IV: Formation of cyclic dimers and linear trimers

Hydrodynamische eigenschaften von methylcellulosen in lösung